This invention is directed to thermoplastic compositions having improved molding capability.
Injection molding provides a convenient way for preparing various articles from thermoplastic resins, particularly objects of a relatively intricate nature. In order to injection mold articles in an economic manner the mold resident cycle time should be kept to a minimum. This shorter cycle time provides a shorter resin heat period with consequently less thermal damage to the resin itself and/or less thermal promoted interaction between the resin and various additives present in the resin. In order to accomplish a release of the resin from the mold, various mold release agents have been found which provide for a release of the resin with lower ejection pressure. Such agents should be chemically compatible with the resin as measured by the usual characteristics of the resin under normal conditions and heat treatments.
Of the thermoplastic resins which find a mold release agent useful from time to time are polycarbonate, copolyestercarbonate and blends of these resins with other thermoplastic resins and impact modifiers. As a result of the generally high temperature which these thermoplastics are subjected to during molding and the inherent sensitivity of these resins to chemical attack and degradation by additives which are often compatible with many other thermoplastics, it is necessary to select mold release agents with high temperature stability and compatibility with polycarbonates.
With molded parts, and particularly injection molded parts, it is very important to be able to eject the part from the mold without damaging the part, while at the same time, maintaining the efficiency and cycle time. To reduce or minimize cycle times, many manufacturers are removing parts at hotter temperatures (that is, not letting them cool as long). Since the temperature is hotter, the part has a tendency to stick more easily in the mold, or become distorted as it is ejected from the mold, since the thermoplastic material is not as stiff as if it were allowed to cool longer. In addition, many parts are becoming more complex as manufacturers try to combine multiple parts into one larger and/or more complex part having more detail and often more potential areas to stick in the mold. Therefore, it is very important to have a thermoplastic material and a combination of mold release agents that allows for the part to be ejected at lower pressures or minimal force without cracking or other part deformation.
There accordingly remains a need in the art for thermoplastic compositions comprising polycarbonates, as well as impact modified polycarbonate blends, having improved molding capability, a good flow and impact balance, and mold release.